Grave-to-cradle photothermal upcycling of waste polyesters over spent LiCoO2

Lithium-ion batteries (LIBs) and plastics are pivotal components of modern society; nevertheless, their escalating production poses formidable challenges to resource sustainability and ecosystem integrity. Here, we showcase the transformation of spent lithium cobalt oxide (LCO) cathodes into photothermal catalysts capable of catalyzing the upcycling of diverse waste polyesters into high-value monomers. The distinctive Li deficiency in spent LCO induces a contraction in the Co−O6 unit cell, boosting the monomer yield exceeding that of pristine LCO by a factor of 10.24. A comprehensive life-cycle assessment underscores the economic viability of utilizing spent LCO as a photothermal catalyst, yielding returns of 129.6 $·kgLCO−1, surpassing traditional battery recycling returns (13–17 $·kgLCO−1). Solar-driven recycling 100,000 tons of PET can reduce 3.459 × 1011 kJ of electric energy and decrease 38,716 tons of greenhouse gas emissions. This work unveils a sustainable solution for the management of spent LIBs and plastics.


Supplementary Note One
Characterizations SEM images were obtained with a Zeiss G500 scanning electron microscopy with a n accelerating voltage of 5 kV.TEM images were captured utilizing a FEI Talos F200X transmission electron microscope, employing an acceleration voltage of 200 kV and employing a Ceta 16 M pixel CMOS camera.Powder X-ray diffraction analysis was conducted using a PANalytical X-ray diffractometer at 40 kV and 40 mA, employing Cu Kα radiation (λ = 1.54056Å).The diffraction patterns were collected in the 2θ range of 5° to 80° with the scanning speed was 2° min −1 .Monitoring of the reaction system's temperature was conducted using a JK804 multi-channel temperature tester.
To characterize the valence states and local structural information of Co atoms, the experiment XAS including XANES and EXAFS spectra at Co K-edge spectra were collected in the transmission modes of room temperature.The cobalt K-edge absorption data were all calibrated and aligned using reference Co metal spectra with the maximum value of the first derivative set to 7709 eV.The temperature-dependent XAS experiment was performed using in-house heating cell with an optimized pellet form of sample.To measured XAS spectra, synthesized powders were ground to fine powders and pressed into pellet prior to the experiment.
The quantification of Li and Co content in the samples was achieved using inductively coupled plasma emission spectrometry (PE Optima 8300).To prepare the ICP-OES samples, the sample (10 mg) is first dissolved in 5 ml of concentrated hydrochloric acid.Subsequently, the solution was diluted in 0.5 wt.% HNO3 to a concentration of 10 ppm, and then the samples were prepared for ICP-OES measurement.
The 1 H and 13 C NMR spectra were obtained using a Bruker Advance III HD-400 MHz spectrometer equipped with a BFO smart probe.11.2 mg of the product and 0.5 mL of d-DMSO were sonicated in an NMR tube until the product dissolved, and 20 μL of dioxane was added as an internal standard.Subsequently, quantitative analysis of the product was performed using where Vdioxane is the volume of dioxane, ρdioxane is the density of dioxane, Mdioxane is the molecular weight of dioxane, MBHET is the molecular weight of BHET, IBHET is the peak area in δ = 8.13 (2H), Idioxane is the peak area in δ = 3.56 (4H).

Thermal catalysis:
In the case of thermal catalysis, the reactor was placed in an oil bath to maintain the reaction temperature at 190 °C.All other steps remained consistent with photothermal catalysis.In the UV light system with thermal catalysis, the reaction conditions involved adding an additional UV light with an intensity of 0.01 W cm −2 to the thermal catalysis.
All other conditions remained consistent with thermal catalysis.The catalytic conditions are listed in Supplementary Table 14.
The PET conversion rate (CPET) and the yield of BHET (YBHET) was calculated based on following equations.
where WPET0, WPETt, and WBHET denote the initial weight of PET, the weight of PET remaining unreacted, and the weight of BHET, respectively.MWPET and MWBHET stand for the molecular weight of the PET repeating unit, 192 g mol -1 , and the molecular weight of BHET, 254 g mol -1 .

Kinetic studies on the PET glycolysis:
The glycolysis of PET can be regarded as a first-order reaction.The reaction equation equations are listed as follows.
()* = C 6789 e %0: (6) Among them, CPET and CPET0 are the concentration of PET at t and 0, respectively; X is the The activation energy (Ea) of the reaction can be calculated using the Arrhenius formula.
where A, R and T refer to the pre-exponential factor, gas constant (8.314J (k•mol) −1 ) and reaction temperature in Kelvin, respectively.Activation energies (Ea) were calculated to be 78.7 and 79.4 kJ mol −1 from the linear Arrhenius plot.

Cycle performance of catalysts:
The experimental procedure followed a standard photothermal catalytic glycolysis protocol.Following the depolymerization step, PET, oligomers, and the catalyst were separated via filtration.The resulting mixture was transferred to a 100 mL beaker, to which 15 mL of N-Methyl-2-pyrrolidone (NMP) was added.The mixture was then heated to 150 °C to ensure complete dissolution of both PET and its oligomers.Subsequently, the catalysts were separated through a hot filtration and washed twice with hot NMP.Throughout the recovery process, there was a marginal loss of catalysts, approximately 15%.To compensate for this loss, fresh catalysts were introduced in the subsequent PET glycolysis cycle.

Long-term stability test:
We carried out five long-term parallel experiments, aiming to simulate extended reaction periods.Each experiment-maintained consistency in terms of the number of reactants (5.0 g PET and 10 g EG), catalyst dosage (1 mg Li0.76CoO2), light intensity (0.63 W cm −2 ), and reaction temperature (170 °C).The sole parameter that varied was the reaction time, set at 5 hours, 10 hours, 20 hours, 40 hours, and 70 hours, respectively.
Outdoor demonstrations: The experimental conditions were precisely controlled as follows: 50 g of PET, 200 g of EG, and 1 g of Li0.76CoO2 were introduced into a custom-made apparatus.
This setup was then exposed to concentrated sunlight for a duration of 20 minutes.The resulting yield of BHET product achieved in this process amounted to 42 g.

Collection and pre-process of real-word plastics:
The collected plastics were subjected to a thorough washing process, involving more than three cycles of rinsing with water.
Subsequently, the cleaned plastics were dried in a forced-air oven.These plastics were then precision-cut into pieces measuring 0.5 × 0.5 cm each.The specific reaction conditions are summarized in the following Supplementary Table 15.We recognize the importance of evaluating the long-term stability of the catalyst comprehensively.To address this, we carried out five long-term parallel experiments, aiming to simulate extended reaction periods.Each experiment maintained consistency in terms of the number of reactants (5.0 g PET and 10 g EG), catalyst dosage (1 mg Li0.76CoO2), light intensity (0.63 W cm −2 ), and reaction temperature (170 °C).The sole parameter that varied was the reaction time, set at 5 hours, 10 hours, 20 hours, 40 hours, and 70 hours, respectively.Notably, to accommodate longer reaction times, we reduced the catalyst dosage to 1 mg while keeping other conditions consistent with the typical reaction conditions.

Economic and Environmental Analysis
In Supplementary Fig. 13a, we present the relationship between the conversion rate and reaction time for the five parallel experiments.The gradual increase in the conversion rate of PET with increasing reaction time is evident.Following the literature, PET glycolysis is typically a first-order reaction.The linear fit of the data from Supplementary Fig. 13a demonstrates a perfect linear relationship (Supplementary Fig. 13b), indicating that the catalyst's activity remains robust even under prolonged illumination.This observation assures us of the catalyst's excellent stability over extended reaction times.Supplementary Fig. 24 Cost breakdown of the rBHET MSP in the base case process design and as a function of plant size.

:
The EverBatt model, developed by the Argonne National Laboratory, was employed to conduct a techno-economic and life-cycle assessment of three distinct methods for recycling spent batteries: pyrometallurgy, hydrometallurgy, and direct cathode recycling.This comprehensive model is designed to evaluate the costs and environmental implications of closed-loop battery recycling processes.In addition, our technoeconomic analysis has included necessary separation processes.The total cost for LCO separation is calculated to be $1.05 per kilogram.Supplementary Fig.13The stability of Li0.76CoO2 with 70 hours of continuous catalytic testing.a, The conversion rates of PET at different times.b, The linear fitting of conversion rate versus reaction time.
conversion rate of PET; k is the conversion rate of PET at t. Effects of reaction temperature on PET glycolysis with different reaction times are shown in Figs.S10.The slope of the straight line represents the corresponding rate constant.For photothermal catalysis, the rate constants (kphotothermal) at 170, 175, 180, 185, and 190 ºC are 0.04547, 0.05613, 0.07047, 0.08909 and 0.11458 h

Table 5
Detailed PDF of PET recovery process section (base case).

Table 6
Yearly operating cost breakdown (base case).Supplementary Table14The summary of reaction conditions for photothermal and thermal catalysis.